Binder-free Electrode Material For Supercapacitors Research Articles

N, O-codoped porous carbon fiber cloth synthesized by molecular dispersed CaCl2·6H2O in situ activation for high performance supercapacitors

In this study, a nitrogen/oxygen co-doped carbon fiber cloth with a hierarchical porous structure was synthesized by one-step carbonization and in situ activation method and acted as binder-free electrode materials for supercapacitors. Cotton fiber cloth served as the carbon precursor, while molecular dispersed CaCl2·6H2O and urea functioned as activator and N dopant, respectively. The influence of molar concentration of CaCl2·6H2O and urea on the microstructure and capacitive performance of the resulting products were investigated. CaCl2·6H2O has an expansion effect on pores, resulting in reduction of micropores. Hence, the specific surface area of the resulting porous carbon increased first and then decreased with the increase of CaCl2·6H2O concentration. In addition, the erosion of NH3 and CO2 (produced by the decomposition of urea) at high temperature on the surface of the samples promoted the formation of porous structure. Urea plays the dual role of doping and activation agent. The morphology and structure analysis shown that the activated samples exhibited hierarchical pore structure, large specific surface area, and high heteroatom content. The optimal sample NAC-20 exhibited good capacitive performance, including high specific capacitance of 260.9 F g−1 at 0.1 A g−1 and good rate performance. Moreover, the symmetric supercapacitor exhibited a maximum energy density and power density of 16.2 Wh kg−1 and 19.0 kW kg−1, respectively, in 6 M KOH electrolyte. In this work, a green, low-cost molten salt activation method was proposed to synthesis biomass derived porous carbon materials for energy storage devices.

Flower-like Heterogeneous Phosphorus-Doped Co3S4@Ni3S4 Nanoparticles as a Binder-free Electrode for Asymmetric All-Solid-State Supercapacitors

Through the hydrothermal method and the gas-phase phosphating method, the flower-like heterogeneous phosphorus-doped Co3S4@Ni3S4 was synthesized in situ on a nickel foam substrate as the binder-free electrode material for supercapacitors. Phosphorus-doped Co3S4@Ni3S4 electrode material combines the merits of transition metal sulfides and 3D porous network heterostructure, showing the excellent theoretical specific capacitance and the high specific surface area. The introduction of phosphorus atoms with an atomic radius larger than sulfur atoms can optimize the internal electronic structure and cause structural distortion. Therefore, the specific capacitance/specific capacity of this electrode can reach 3614 F g–1 (451 mAh g–1) at 1 A g–1 and still maintain the initial specific capacitance of 73% after 3000 cycles. The assembled P–Co3S4@Ni3S4-175//AC ASC device exhibits an ultra-high energy density of 72 Wh kg–1 at a power density of 800 W kg–1. Meanwhile, it can show extraordinary cyclic stability, with a retention rate of 91% after 5000 cycles. This work provides a feasible synthesis method to prepare the composite electrode materials for supercapacitors.

Manganese-doped tungsten disulfide microcones as binder-free electrode for high performance asymmetric supercapacitor

Manganese-doped tungstate sulfide (Mn-WS2) microcones were developed with varying levels of Mn, grown directly on electrically conductive Ni foam, and used as binder-free electrode material for supercapacitors. The experimental research indicates that Mn-WS2 microcones has significantly improved electrochemical activity and cyclic stability compared with pure WS2 due to additional ion diffusion channels. A strong synergy between the transitional metal ions in Mn-WS2 remarkably improved the redox activity, rate capability, and cycling stability. The Mn-WS2 microcones had a high specific capacitance of 107.79 mA h g−1 at 1 A g−1, a high rate capability of 75.18% at 20 A g−1, and 96.1% capacitance retention after 10,000 charge–discharge cycles. The effect of Mn ions on the electrochemical performance of WS2 microcones was also studied in detail. The enhanced electrochemical performance of the electrode can be attributed to the unique structural features of WS2 microcones arrays grown in Ni foam, which allow the surface of WS2 to be highly accessible to electrolyte ions. Furthermore, an all solid state asymmetric supercapacitor (ASCs) assembled with Mn-WS2 microcones as anode and GO/Fe3O4 cathode (Mn-WS2//PVA-KOH// GO/Fe3O4) delivered high specific energy of 70.65 W h kg−1 at 997.41 W kg−1. These results confirm that Mn-WS2 with outstanding electrochemical properties could be a promising electrode material for practical application in electrochemical energy storage field.

Monolithic Carbon Spherogels as Freestanding Electrodes for Supercapacitors

This study presents a direct application for freestanding and monolithic carbon spherogels, which are highly porous carbon aerogels solely composed of hollow nanospheres, as binder-free electrode materials for supercapacitors. By applying polystyrene nanospheres as templating agents in the size range of 277–907 nm and concentrations from 1.5 to 12 wt % in the sol–gel polymerization process of resorcinol–formaldehyde, we can distinctly tailor the hollow spheres’ pore arrangement and thickness of the microporous carbon walls. Furthermore, the required synthesis conditions for mechanically processable (sliceable) carbon spherogels are explored. Following physical activation with carbon dioxide, only 277 nm templated samples, featuring one thin-walled (<20 nm) and one thick-walled (>60 nm) variant, retain a freestanding bulk constitution and hence are suitable for the application as binder-free electrodes. The electrochemical evaluation demonstrates the advantage of hollow carbon sphere aerogels in comparison to conventional carbon aerogels with respect to capacitance, particularly at high scan rates. The analysis of the electrolyte diffusion kinetics and the network morphology after 10,000 charge/discharge cycles reveals the necessity of wall thickness optimization. Thick-walled variants are favored due to a much higher rate capability of 30 kW kg–1 compared to 10 kW kg–1). Additionally, a post-mortem TEM analysis reveals the loss of a central cavity and sphere degradation in thin-walled samples.

Electrospun flexible lignin/polyacrylonitrile-based carbon nanofiber and its application in electrode materials for supercapacitors

In this study, a lignin/polyacrylonitrile (PAN) composite nanofiber membrane is prepared by electrospinning and used as the precursor to prepare flexible carbon nanofibers (CNFs) through pre-oxidation and carbonization. The micromorphology, crystal structure, pore size distribution and specific surface area of the CNFs are characterized by field emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy and specific surface adsorption analysis, respectively. The electrochemical properties of the CNF membrane are also investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy due to its potential application in binder-free electrode materials for supercapacitors. We successfully prepared flexible CNFs with an average diameter of about 539 nm and a specific surface area of 1053.78 m2/g when the mass ratio of lignin to PAN was 9:1 in a solution concentration of 28 wt%. The CNFs are loaded onto nickel foam to prepare the electrode materials for supercapacitors without a binder. When the current density is 0.5 A/g, the specific capacitance could be up to 201.27 F/g and the equivalent series resistance is only 0.57 Ω, which shows an excellent electrochemical performance. This study not only provides a theoretical basis for the high-value utilization of lignin and the preparation of flexible lignin/PAN-based CNFs, but also provides a new type of environmentally friendly raw material for the electrodes of supercapacitors and could be helpful to alleviate the energy crisis and environmental pollution.

Porous graphene oxide nanosheets warped by Ni(OH)2 platelets as an efficient binder-free electrode material for supercapacitors

This article describes synthesis of the nickel hydroxide nanostructures (Ni(OH)2)@porous reduced graphene oxide (p-RGO) on 3-D nickel foam (NF) through a cost-effective one-step electrochemical strategy. This method composed of electrophoretic deposition of porous RGO plates and in situ formation of hydroxide nanostructures onto NF electrode. For comparison, the pristine Ni(OH)2/NF electrode was also fabricated via the similar method. The prepared nano-composite structure showed high surface area of 269.3 m2 g–1 with mesoporous texture and mean pore diameter of 3.58 nm, where the pure Ni hydroxide exhibited only surface area of 73.5 m2 g–1 and pore diameter of 2.75 nm. Both prepared samples were characterized via XRD, IR, FE-SEM, Raman, BET, TGA/DSC and TEM analyses. The nickel hydroxide@p-RGO composite deposited onto NF electrode has high specific capacitances as well as high electrical conductivity, where it delivered higher capacity of 1792 F g–1 at a current load of 2 A g–1 when compared with the Ni(OH)2 electrode (1175 F g–1 at the same current density), which nearly 65 % increment in capacity was observed. The composite material exhibited an outstanding capacity retention of ∼95.3 % and 87.6 % after 4000 cycles at the current densities of 1 and 7 A g–1, respectively. This methodology provides a feasible route for preparation of the metal hydroxide/graphene hybrid materials for electrochemical energy storage applications.

High energy density hybrid supercapacitor based on 3D mesoporous cuboidal Mn2O3 and MOF-derived porous carbon polyhedrons

Nowadays, it is highly desired to design and fabricate efficient and cost-effective electrode materials for energy conversion and storage devices. Manganese oxides are remarkable electrode material for pseudocapacitors due to their ideal capacitive behaviour, low cost and environmental friendliness. However, low conductivity and poor cycling stability remain major challenges for their commercialization. Herein, we demonstrate the direct growth of mesoporous cuboidal Mn2O3 via a one-step hydrothermal approach on the highly conductive surface of nickel foam (Mn2O3@NF) as a high-performance binder-free electrode material for supercapacitors(SCs). The as-prepared cuboidal Mn2O3 possesses high specific surface area and mesoporous feature which lead to larger number of active sites and improve the electrochemical storage activity. As a result, excellent pseudocapacitive performance is achieved with remarkably enhanced capacitance of 791 Fg-1 at 5 mVs-1 and good cycling stability is observed with retaining 92.5% of its initial capacitance after 5000 continuous charging-discharging cycles. Furthermore, a hybrid SC has been fabricated using Mn2O3@NF as a positive electrode and metal-organic framework (MOF) derived mesoporous carbon as a negative electrode. The hybrid Mn2O3@NF//MC device can operate with a large working potential window of 0.0–1.6 V, which leads to a specific energy density of 112.82 Wh kg−1 at a moderate power density of 320 W kg−1 and also exhibits excellent cycling capability with retaining 86.73% of the original capacitance after 5000 cycles, which is comparable than most of previously reported manganese oxide based SCs. The experimental results show that the Mn2O3@NF can offer great potential for practical energy storage applications.

Wood-Derived Ultrathin Carbon Nanofiber Aerogels.

Carbon aerogels with 3D networks of interconnected nanometer-sized particles exhibit fascinating physical properties and show great application potential. Efficient and sustainable methods are required to produce high-performance carbon aerogels on a large scale to boost their practical applications. An economical and sustainable method is now developed for the synthesis of ultrathin carbon nanofiber (CNF) aerogels from the wood-based nanofibrillated cellulose (NFC) aerogels via a catalytic pyrolysis process, which guarantees high carbon residual and well maintenance of the nanofibrous morphology during thermal decomposition of the NFC aerogels. The wood-derived CNF aerogels exhibit excellent electrical conductivity, a large surface area, and potential as a binder-free electrode material for supercapacitors. The results suggest great promise in developing new families of carbon aerogels based on the controlled pyrolysis of economical and sustainable nanostructured precursors.

Influence of Ti3C2Tx (MXene) intercalation pseudocapacitance on electrochemical performance of Co-MOF binder-free electrode

In this paper, we reported a synthesis of cobalt metal-organic framework spheres (Co-MOF) and Co-MOF/titanium carbide (Ti3C2Tx) directly on Ni foam, which could be utilized as a novel binder-free electrode material for supercapacitors. The influence of intercalation pseudocapacitance between Ti3C2Tx and Co-MOF on Ni foam was evaluated by various electrochemical techniques. The as-prepared mesoporous electrodes exhibited outstanding electrochemical performance in 3 M KOH electrolyte. A maximum gravimetric capacitance of 2872.5 F g−1 and 3741 F g−1 were obtained for Co-MOF@Ni and Co-MOF/Ti3C2Tx@Ni, respectively. The voids in the Co-MOF and the good conductivity of layered Ti3C2Tx enhanced the active sites and afforded fast ion transport. This work provides a new direction to promote the Ti3C2Tx based materials for high-performance binder-free supercapacitor electrodes.

In situ hydrothermal preparation of mesoporous Fe3O4 film for high-performance negative electrodes of supercapacitors

A mesoporous Fe3O4 film was prepared as binder-free electrode material for supercapacitors through a facile process that included the hydrothermal electroplating of an Fe/Zn alloy, in situ electrolytic dealloying to remove the Zn template, and oxidation in a water vapor environment. The Fe3O4 film showed a cubic structure and mesoporosity with a specific surface area of 247 m2 g−1. As a negative electrode material, the mesoporous Fe3O4 film delivered a high gravimetric capacity of 221 C g−1 at 1 A g−1, and the gravimetric capacity was maintained at 154 C g−1 even at a high current density of 50 A g−1. In addition, the mesoporous Fe3O4 electrode exhibited very high cycling stability (only 4.7% capacity loss after 10,000 galvanostatic charge–discharge cycles). Electrochemical impedance spectroscopy revealed that the mesoporous Fe3O4 film had excellent conductivity, implying its promising application as a supercapacitor electrode.

Hierarchical graphite foil/CoNi2S4 flexible electrode with superior thermal conductivity for high-performance supercapacitors

Effective heat dissipation is a crucial issue in electrochemical energy storage devices. Thus, it is highly desirable to develop high-performance electrode materials with high thermal conductivity. Here, we report a facile one-step electrodeposition method to synthesize ternary cobalt nickel sulfide (CoNi2S4) flower-like nanosheets which are grown on graphite foil (GF) as binder-free electrode materials for supercapacitors. The as-fabricated GF/CoNi2S4 integrated electrode manifested an excellent thermal conductivity of 620.1 W·m−1·K−1 and a high specific capacitance of 881 F·g−2 at 5 mA cm−2, as well as good rate capability and cycling stability. Ultimately, the all-solid-state symmetric supercapacitor based on these advanced electrodes demonstrated superior heat dissipation performance during the galvanostatic charge-discharge processes. This novel strategy provides a new example of effective thermal management for potential applications in energy storage devices.

Novel binder-free electrode materials for supercapacitors utilizing high surface area carbon nanofibers derived from immiscible polymer blends of PBI/6FDA-DAM:DABA

High performing supercapacitor electrode materials were obtained by controlling the nanostructure of electrospun fibers derived from PBI/6FDD immiscible blends.

Three-dimensional Nitrogen-doped graphene as binder-free electrode materials for supercapacitors with high volumetric capacitance and the synergistic effect between nitrogen configuration and supercapacitive performance

Three dimensional nitrogen-doped graphene (3DNG) with high nitrogen content and improved electrochemical performance is successfully prepared by a facile, lost-cost hydrothermal method with ammonia as reducing-doping agent. The as-prepared 3DNG exhibits a hierarchical and interconnected porous network, which offers favorable pathways for electrolyte penetration and transportation. Remarkably, as binder-free electrode in aqueous electrolyte, the resultant 3DNG-2 with both high nitrogen content (7.71 at%) and large active material density (1.31gcm−3) exhibits an ultrahigh volumetric capacitance of 437.5Fcm−3 (334.0Fg−1) at current density of 0.5Ag−1 and superior cycling stability (93% capacitance retention after 20 000 cycles at high current density of 10Ag−1). Further analyses indicate that the N-configurations are of great significance to the improvement of electrochemical behavior as well as the N-content. This work provides an effective way to synthesize 3DNG with excellent electrochemical properties for high performance supercapacitor and promotes the in-depth understanding of the enhancement mechanism of N-doping to supercapacitor performance.

In situ two-step electrochemical preparation of fluoride-free nickel-based compound film on nickel plate for supercapacitors

A nickel-based compound layer was prepared on a nickel plate by anodization in a 75 wt% H3PO4 solution containing NH4F. This layer was then treated by galvanostatic charge/discharge (GCD) until a black outer layer was detached, leaving behind a film on the nickel plate as a binder-free electrode material for supercapacitors. The microstructural characterization shows that the film consists of Ni(OH)2 and NiO, and no fluoride is found in the as-obtained film. Electrochemical tests demonstrate that this fluoride-free film electrode exhibits a high capacitance of 954 F·g−1 at 7.5 A·g−1, excellent rate capability (a 19.5 % capacitance reduction with the current density increasing to 120 A·g−1) and cycling stability. Within 3500 cycles, the specific capacitance does not decrease, but rather increases from 840 F·g−1 to approximately 1092 F·g−1 in the first 100 cycles at 60 A·g−1, and remains stable until the aforementioned layer is detached.

Application of biomass-derived flexible carbon cloth coated with MnO2 nanosheets in supercapacitors

Successful application of inexpensive energy storage devices lies in the exploitation of fabrication approaches that are based on cost-efficient materials and that can be easily scaled up. Here, inexpensive textile weaved by natural flax fiber is selected as raw material in preparing flexible and binder-free electrode material for supercapacitors. Although carbon fiber cloth obtained from the direct carbonization of flax textile exhibits a low specific capacitance of 0.78 F g−1, carbon fiber cloth electrode shows a very short relaxation time of 39.1 m s and good stability with almost 100% capacitance retaining after 104 cycles at 5 A g−1. To extend the application of the resulting carbon cloth in supercapacitor field, a layer of MnO2 nanosheets is deposited on the surface of carbon fiber via in situ redox reaction between carbon and KMnO4. The specific capacitance of MnO2 reaches 683.73 F g−1 at 2 A g−1 and still retains 269.04 F g−1 at 300 A g−1, indicating the excellent rate capacitance performance of the carbon cloth/MnO2 hybrids. The present study shows that carbon cloth derived from flax textile can provide a low-cost material platform for the facile, cost-efficient and large scale fabrication of binder-free electrode materials for energy storage devices.

Ni3S2 coated ZnO array for high-performance supercapacitors

In this communication, for the first time, we demonstrate the electrodeposition of Ni3S2 on ZnO (ZnO@Ni3S2) array supported on nickel foam. We further demonstrate the direct use of ZnO@Ni3S2 array as a binder-free electrode material for supercapacitors and this electrode exhibits a very high specific capacitance of 1529 F g−1 at a current density of 2 A g−1, good rate capability and cycling stability.

Supercapacitors based on 3D network of activated carbon nanowhiskers wrapped-on graphitized electrospun nanofibers

Due to their cycling stability and high power density, the supercapacitors bridge the power/energy gap between traditional dielectric capacitors and batteries/fuel cells. Electrode materials are key components for making high performance supercapacitors. An activated carbon nanowhiskers (ACNWs) wrapped-on graphitized electrospun nanofiber (GENF) network (ACNWs/GENFN) with 3D porous structure is prepared as a new type of binder-free electrode material for supercapacitors. The supercapacitor based on the ACNWs/GENFN composite material displays an excellent performance with a specific capacitance of 176.5 F g−1 at current density of 0.5 A g−1, an ultrahigh power density of 252.8 kW kg−1 at current density of 800 A g−1 and an outstanding cycling stability of no capacitance loss after 10,000 charge/discharge cycles.

Fabrication of Ni(OH)2 nanoflakes array on Ni foam as a binder-free electrode material for high performance supercapacitors

The present communication reports on the first preparation of Ni(OH)2 nanoflakes array on Ni foam, carried out by hydrothermal treatment of Ni foam in acidic medium without the presence of extra nickel salt. We further demonstrate the application of such Ni(OH)2/Ni foam as a binder-free electrode material for supercapacitors. It is found that it can deliver high capacities of 1228F/g and 918F/g at 5A/g and 30A/g, respectively, with excellent cycling stability.

Poly(p-phenylenediamine)/graphene nanocomposites for supercapacitor applications

Herein, we report new nanocomposite materials based on poly(p-phenylenediamine) (PpPD) and hydrogen exfoliated graphene (HEG) sheets as efficient binder-free electrode materials for supercapacitors. The nanocomposites are synthesized via chemical oxidative polymerization of a para-phenyldiamine monomer in the presence of graphene sheets in acidic medium. The initial weight ratio of monomer to graphene is varied to get nanocomposites of different polymer to graphene weight ratios. The electrochemical performances of these nanocomposites as a supercapacitor electrode are investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques in two electrode configuration. The nanocomposite with polymer to graphene weight ratio 1 : 2 shows a maximum specific capacitance of 248 F g−1 at a specific current density of 2 A g−1 and also demonstrates high rate capability. The maximum energy density of the fabricated symmetrical supercapacitor cells based on the mass of active electrodes is calculated to be 8.6 W h kg−1 and 5.8 W h kg−1 at a power density of 0.5 kW kg−1 and 5 kW kg−1, respectively. The nanocomposites retain 72% of their initial capacitance after 1000 cycles of charge–discharge at a high specific current density of 10 A g−1.

Conducting polymer/carbon nanocoil composite electrodes for efficient supercapacitors

Herein, we report for the first time, conducting polymer (polyaniline (PANI) and polypyrrole (PPY)) coated carbon nanocoils (CNCs) as efficient binder-free electrode materials for supercapacitors. CNCs act as a perfect backbone for the uniform distribution of the conducting polymers in the composites. In two electrode configuration, the samples exhibited high specific capacitance with the values reaching up to 360 and 202 F g−1 for PANI/CNCs and PPY/CNCs respectively. The values obtained for specific capacitance and maximum storage energy per unit mass of the composites were found to be comparable to one of the best reported values for polymer coated multi-walled carbon nanotubes. In addition, the fabricated PANI/CNC based supercapacitors exhibited a high value of 44.61 Wh kg−1 for maximum storage energy per unit mass. Although the devices exhibit an initial capacitance loss due to the instability of the polymer, the specific capacitance stabilizes at a fixed value after 500 charge–discharge cycles.